Difficulties are encountered in practice in the treatment of contaminated water flows such as sewage prior to fine filtration, due to the presence of heavy and generally untreatable objects such as rags, string, plastic bags, and the like.
If such items are not removed then proper and adequate treatment of the liquid does not result, and blockage of ducts and channels may occur.
A screening device is known comprising a continuously movable endless conveyor loop formed of a series of interconnected link pieces each having a lifting hook on which material to be screened is collected during movement through the contaminated water flow, and a rearwardly extending bar linkage.
The link pieces are mounted for rotatable movement on support rods extending across the width of the band conveyor loop such that as the link pieces are caused to rotate by means of a forced change in direction of travel of the loop, the books of the link pieces cooperate with the bar linkages of other link pieces, such that the bar linkages act to clear the hooks of collected material.
In addition a four armed rotating brush is used to clean the bar linkages of collected grease and similar unwanted deposits.
Whilst being effective, the prior art just described is complicated in design and costly to manufacture. It also requires the presence of two independently operable mechanical means to maintain the operating parts clean and free from contamination matter which builds up over time thereby reducing overall efficiency.